Extra vitamin D "was associated with significantly less physical, emotional and general fatigue, greater quality of life and the ability to perform activities of daily living," said Tara Raftery, a research dietitian and doctoral candidate at Trinity College Dublin. She is scheduled to present the findings Saturday at the Digestive Disease Week meeting in Orlando, Fla.

Raftery and her colleagues evaluated 27 patients who had Crohn's in remission. (Even in remission, fatigue and quality of life can be problematic.) The patients were assigned to take either 2,000 IUs (international units) of vitamin D a day or a dummy vitamin for three months.

Before and after the study, the researchers measured hand-grip strength, fatigue, quality of life and blood levels of vitamin D.

"Hand-grip strength is a proxy measure of muscle function," Raftery said. "Muscle function has been known to be reduced in Crohn's disease."

Besides boosting bone growth and remodeling, vitamin D is thought to improve neuromuscular and immune function, reduce inflammation and help with other bodily tasks. Children and adults aged 1 year to 70 are advised to get 600 IUs a day; older adults, 800, according to the U.S. National Institutes of Health (NIH).

Vitamin D is found in fatty fish such as salmon, in smaller amounts in cheese, egg yolks and beef liver, and in fortified foods such as milk.

Sometimes called the sunshine vitamin, vitamin D is also produced when the sun's rays strike the skin.

Crohn's can affect any part of the gastrointestinal tract, but most commonly affects the end of the small bowel and the beginning of the colon. Symptoms vary, but may include persistent diarrhea, rectal bleeding, abdominal cramps, and pain and constipation. About 700,000 Americans are affected, according to the Crohn's & Colitis Foundation of America.

Its cause is not well understood, but Crohn's is thought to involve heredity and environmental factors. Experts believe that in those with Crohn's, the immune system attacks harmless intestinal bacteria, triggering chronic inflammation and, eventually, the disease symptoms.